Chloro Fluoro Carbons (CFCs) have heretofore been used as a detergent and a refrigeration medium. However, in recent years, an increasing attention has been paid to a problem of pollution nuisance in a global environment and restriction of the use of CFCs has been universally acceded to. Therefore, alternatives of CFCs have been intensively investigated and developed. Especially chlorine-free fluorinated saturated hydrocarbons attract public attention from a viewpoint of environmental protection because there is no problem of depletion of the ozone layer.
For example, fluorinated saturated hydrocarbons represented by the following formula (2): ##STR2## wherein R and R' represent a perfluoroalkyl group, or both R and R' are bonded together to form a perfluoroalkylene group which is a part of a ring, are expected to be used as detergents, solvents, propellants, and heating media for heat pumps. As a specific example of the fluorinated saturated hydrocarbons, 1,1,2,2,3,3-hexafluorocyclopentane is described as a detergent in U.S. Pat. No. 5,084,199.
As means for producing fluorinated saturated hydrocarbons which are expected to be widely used in future, a process is generally known wherein a corresponding unsaturated hydrocarbon having chlorine or bromine bonded to the carbon-to-carbon double bond is allowed to react with hydrogen in the presence of a base such as a basic alkali metal salt or amine by using a palladium catalyst or a nickel catalyst (for example, DE-A-3,735,467 and U.S. Pat. No. 5,084,199). As specific example of such process, there can be mentioned a process wherein 1,2-dichloro-3,3,4,4,5,5-hexafluoro-cyclopentene is hydrogenated in the presence of triethylamine by using a Raney nickel catalyst to produce 1,1,2,2,3,3-hexafluorocyclopentane, and a process wherein 1,2-dichloro-3,3,4,4,5,5-hexafluoro-cyclopentene is hydrogenated in the presence of sodium acetate by using a palladium catalyst to produce 1,1,2,2,3,3-hexafluorocyclopentane. However, these processes have problems in economy and operating characteristics because acidic substances such as hydrogen chloride or hydrogen bromide produced as by-products are deposited as an alkali metal salt or an amine salt and thus an operation of separating the target substance is indispensable.